So, this is a very interesting question - because the resolution of the top screen is different than that of the DS, some games look exactly the same, and some games have minor blemishes. For example, the text in Pokemon Black looks completely odd on a 3DS, but my playthrough of Radiant Historia looks fine. If you want to, you can set the 3DS to load the title in its original resolution, but you then get a smaller screen area to play on.